This invention relates to improved biaxially oriented, heatset hollow containers wherein the containers are made of a material comprising an intimate fusion blend of poly(ethylene terephthalate) and a high barrier copolyester formed from isophthalic or terephthalic acid, ethylene glycol and 1,3, bis(2-hydroxyethyoxy)benzene.
Polyester containers, particularly those made from poly(ethylene terephthalate), are well-suited for packaging of soft drink beverages, especially in large size containers, such as 2 liter sizes. However, there is a need in the industry to provide a polyester container with longer shelf life, especially small size containers.
Polyester containers made from poly(ethylene terephthalate) do not have sufficient thermal stability or gas barrier properties for use in packaging hot fill or oxygen sensitive foods. Therefore, there is also a commercial need to extend the application of containers made from poly(ethylene terephthalate) to packaging oxygen sensitive foods and to packaging hot fill foods or foods requiring pasturization or sterilization.
In order to improve the physical properties of polyester containers various polymers have been admixed with polyesters in an attempt to improve container gas barrier properties performance. However, such admixtures generally show moisture sensitivity, are not optically clear upon blowmolding and are not sufficiently thermally stable for use in hot fill applications.
The copending application, Ser. No. 631,263, now U.S. Pat. No. 4,578,295, discloses a container formed from a blend of two different polyester materials comprising an admixture of a poly(ethylene terephthalate) and a preferred copolyester of isphthalic or terephthalic acid, ethylene glycol and 1,3 bis(2-hydroxyethoxy)benzene. The container was formed using a conventional blowmolding process. However, such containers are not suitable for use in packaging hot food items since the blended composition of the plastic containers has a low onset-of-shrinkage temperature of about 60.degree. C. The low thermal stability of such blended composition is generally too low for most hot fill food processing and packaging uses.
We have found a commercial solution to these problems. We have discovered that an article made from an intimate fusion blend of poly(ethylene terephthalate) and the high gas barrier copolyester formed from isophthalic or terephthalic cid, ethylene glycol and 1,3,bis(2-hydroxyethoxy)benzene, when made using a blowmolding and heatsetting process provides an improved article having high gas barrier properties and high thermal stability while retaining optically clarity and maintaining advantageous mechanical strength properties.